Plastic optical waveguides, made of a non-elastomeric thermoplastic polymer such as polymethyl methacrylate are known and used. However, any waveguide made of an elastomer having elasticity has not been practically used. One of the reasons for this is that the elastomer has a large attenuation of light transmission due to the method of manufacturing the elastomer.
To impart elasticity to liquid siloxane polymer, a cross-linking agent and/or a cross-linking aid are usually added to the polymer, or the polymer is heated. The addition of the cross-linking agent and/or the cross-linking aid, however, increases the attenuation of light transmission. Further heat treatment of the polymer causes irregularities such as peeling at an interface between a cladding and a core due to thermal shrinkage, thereby the attenuation of light transmission is increased.